The present invention relates to a sintered compact that is used for the production of a magnetic thin film in a thermally assisted magnetic recording media, and to a method of producing such a sintered compact.
In the field of magnetic recording as represented with hard disk drives, a material that is based on a ferromagnetic metal such as Co, Fe, or Ni is being used as the material of a magnetic thin film in a magnetic recording medium. For example, a Co—Cr-based or a Co—Cr—Pt-based ferromagnetic alloy having Co as its main component has been used for the magnetic thin film of a hard disk that adopts the longitudinal magnetic recording system. Moreover, a composite material made from a Co—Cr—Pt-based ferromagnetic alloy having Co as its main component and nonmagnetic inorganic grains is often used for the magnetic thin film of a hard disk that adopts the perpendicular magnetic recording system which has been put into practical use in recent years. In addition, these magnetic thin films are often produced by sputtering a sputtering target made from the foregoing materials using a DC magnetron sputtering equipment in light of its high productivity.
The recording density of hard disks is rapidly increasing year by year, and the current surface density of 600 Gbit/in2 is expected to reach 1 Tbit/in2 in the future. When the recording density reaches 1 Tbit/in2, the size of the recording bit will fall below 10 nm. In such a case, it is anticipated that the superparamagnetization caused by thermal fluctuation will become a problem, and it is further anticipated that the currently used materials of a magnetic recording medium; for instance, a material with higher magnetic crystalline anisotropy obtained by adding Pt to a Co—Cr-based alloy; will no longer be sufficient. This is because magnetic grains, which stably behave as a ferromagnetic at a size of 10 nm or less, need to possess even higher magnetic crystalline anisotropy.
Based on the reasons described above, an FePt phase having an L10 structure is attracting attention as a material for use in an ultrahigh density recording medium. Since an FePt phase yields superior corrosion resistance and oxidation resistance in addition to having high magnetic crystalline anisotropy, it is expected to become a material that can be suitably applied for a magnetic recording medium. Furthermore, in connection with using the FePt phase as a material for use in an ultrahigh density recording medium, demanded is the development of technology for dispersing the ordered FePt magnetic grains, in a magnetically isolated state, while densely aligning the orientation thereof as much as possible.
In light of the foregoing circumstances, a magnetic thin film having a granular structure in which the FePt magnetic grains having an L10 structure are isolated through the interposition of nonmagnetic materials such as oxides and carbon is being proposed for use in a magnetic recording medium of next-generation hard disks adopting the thermally assisted magnetic recording system. This magnetic thin film has a granular structure in which the magnetic grains are magnetically insulated from each other through the interposition of nonmagnetic substances. Generally speaking, this kind of granular structure magnetic thin film is deposited using a sputtering target of Fe-based magnetic material sintered compact.
With regard to a sputtering target of Fe-based magnetic material sintered compact, the present inventors have previously disclosed a technology relating to a sputtering target of ferromagnetic material sintered compact which is configured from a magnetic phase such as an Fe—Pt alloy, and a nonmagnetic phase which separates the magnetic phase, and in which a metal oxide is used as one of the nonmagnetic phase materials (Patent Document 1).
Moreover, Patent Document 2 discloses a sputtering target for use for film deposition for a magnetic recording medium, which is made from a sintered compact having a structure in which a C layer is dispersed in an FePt alloy phase. Moreover, Patent Document 3 discloses a magnetic material sputtering target containing B, and the remainder being one or more elements selected from Co, Fe, and Ni. Moreover, Patent Document 4 discloses a sputtering target for a recording medium, which is configured from one or more elements selected from Fe and Co, and one or more elements selected from Pt and Pd, and in which the oxygen content is 1000 ppm or less. Moreover, Patent Document 5 discloses a target for use in forming a permalloy film, which is made from a sintered compact composed of nickel in an amount of 78 to 85 wt %, and the remainder being iron, and in which the concentration of oxygen as an impurity is 25 ppm or less. In addition, Patent Document 6 discloses a Ni—Fe alloy sputtering target for forming a magnetic thin film, in which the oxygen content is 50 ppm or less.
Meanwhile, since Fe as a magnetic material tends to become ionized, Fe easily reacts with oxygen in the atmosphere or in an atmosphere containing oxygen to form an iron oxide. Nevertheless, since iron oxide is extremely brittle, when iron oxide exists in the sintered compact, there is a problem in that the iron oxide causes the machinability of the sintered compact to deteriorate considerably due to the generation of cracks or chipping when the sintered compact is processed into a sputtering target or the like, and consequently deteriorates the yield. In particular, when a sinter resistance material such as C or BN exists in the sintered compact, there is a problem in that the machinability will deteriorate even further in comparison to the sintered compacts which are based on other components.    Patent Document 1: International Publication No. WO2012/029498    Patent Document 2: JP 2012-102387 A    Patent Document 3: International Publication No. WO2011/070860    Patent Document 4: JP 2003-313659 A    Patent Document 5: JP H07-026369 A    Patent Document 6: JP H11-335821 A